The present invention relates to priority control technology for packet data transmissions in a multiplexer such as ATM (Asynchronous Transfer Mode) multiplexer or IP (Internet Protocol) multiplexer.
There has heretofore been known an ATM multiplexer or IP multiplexer (hereinbelow, generally termed “multiplexer”) which assembles data sent from a plurality of terminal side lines, into ATM cells or IP packets (hereinbelow, generally termed “packet data”) and transmits the packet data onto an ATM line or IP network (hereinbelow, generally termed “network side line”), and which restores packet data sent from on the network side line and transmits the restored data to the plurality of terminal side lines.
Hitherto, in the multiplexer of this type, the priority control of the packet data transmissions onto the network side line has been performed in the following way:
Priority levels are previously assigned to the respective terminal side lines in accordance with the classes etc. of terminals which are connected to the terminal side lines. Besides, when packet data has been generated, it is assigned the priority level which is assigned to the source terminal side line of data stored in this packet data. In the presence of a plurality of items of packet data which are to be transmitted onto the network side line, the packet data to which a higher priority level is assigned and which has been generated earlier is transmitted onto the network side line in preference to the other packet data.
With the above prior art, in a case, for example, where a plurality of terminal side lines of different transmission speeds having an identical priority level are accommodated, and where the transmission speeds of the plurality of terminal side lines are higher than the transmission speed of a network side line, there arises the problem that opportunities for packet data transmissions cannot be equally afforded to the plurality of terminal side lines.
It is assumed that by way of example a case where, during a time period in which packet data can be transmitted onto the network side line once, packet data are generated 9 times on the basis of data sent from the first terminal side line assigned the highest priority level, while packet data is generated once on the basis of data sent from the second terminal side line assigned the same highest priority level. In this case, in a time period in which packet data can be transmitted onto 10 times, 9 times among the 10 times are used for the transmissions of the packet data based on the data sent from the first terminal side line, while only one remaining time is used for the transmission of the packet data based on the data sent from the second terminal side line. As a result, notwithstanding that the same priority level is assigned, the second terminal side line is given the smaller number of opportunities as compared with the first terminal side line with regard to the transmissions of the packet data.